ObjectSpace.count_objects

static VALUE
count_objects(int argc, VALUE *argv, VALUE os)
{
    struct count_objects_data data = { 0 };
    VALUE hash = Qnil;
    VALUE types[T_MASK + 1];

    if (rb_check_arity(argc, 0, 1) == 1) {
        hash = argv[0];
        if (!RB_TYPE_P(hash, T_HASH))
            rb_raise(rb_eTypeError, "non-hash given");
    }

    for (size_t i = 0; i <= T_MASK; i++) {
        // type_sym can allocate an object,
        // so we need to create all key symbols in advance
        // not to disturb the result
        types[i] = type_sym(i);
    }

    // Same as type_sym, we need to create all key symbols in advance
    VALUE total = ID2SYM(rb_intern("TOTAL"));
    VALUE free = ID2SYM(rb_intern("FREE"));

    rb_gc_impl_each_object(rb_gc_get_objspace(), count_objects_i, &data);

    if (NIL_P(hash)) {
        hash = rb_hash_new_capa(2 + T_MASK);
    }
    else if (!RHASH_EMPTY_P(hash)) {
        rb_hash_stlike_foreach(hash, set_zero, hash);
    }
    rb_hash_aset(hash, total, SIZET2NUM(data.total));
    rb_hash_aset(hash, free, SIZET2NUM(data.freed));

    for (size_t i = 0; i <= T_MASK; i++) {
        if (data.counts[i]) {
            rb_hash_aset(hash, types[i], SIZET2NUM(data.counts[i]));
        }
    }

    return hash;
}